Rotary internal combustion engine

ABSTRACT

A rotary internal combustion engine and particularly an improved rotor construction for such engine and method of making is disclosed. A coating system is applied at least to the flank surfaces of the rotor which face the variable volume combustion chambers of the engine, the system serving to reduce heat flow to the oil lubrication system within the rotor and to quench heat build-up on the above surfaces to prevent pre-ignition. The engine is permitted to run at a somewhat higher operating temperature resulting in increased efficiency, better fuel comsumption and reduction of emissions.

United States Patent [1 1 4! ROTARY INTERNAL COMBUSTION ENGINE [75] Inventor: James C. Uy, Dearborn Heights,

Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: Dec. 26, 1973 21 Appl. No.2 428,530

[52] US. Cl 418/179; 123/801 [51] Int. Cl. F0lc 21/00 [58] Field of Search 418/178, 179; 117/71 M; 123/801 [56] References Cited UNITED STATES PATENTS 2,696,662 12/1954 LeSech 117/71 M 3,293,064 12/1966 Aves 117/71 M 3,359,956 12/1967 Bentele. 418/179 3,554,677 1/1971 Zapf 418/178 [1 1 3,888,606 [451 June 10, 1975 3,780,163 5/1973 Elsbett 123/32 B Primary Examiner-C. .I. Husar Assistant ExaminerL. J. Casaregola Attorney, Agent, or Firm.loseph W. Malleck', Keith L. Zerschling [57] ABSTRACT A rotary internal combustion engine and particularly an improved rotor construction for such engine and method of making is disclosed. A coating system is applied at least to the flank surfaces of the rotor which face the variable volume combustion chambers of the engine, the system serving to reduce heat flow to the Oil lubrication system within the rotor and to quench heat build-up on the above surfaces to prevent preignition. The engine is permitted to run at a somewhat higher Operating temperature resulting in increased efficiency, better fuel comsumption and reduction of emissions.

3 Claims, 5 Drawing Figures I ROTARY INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION The unique design of a Wankel rotary engine creates some special problems with respect to heat dissipation. Conventionally, excessive heat absorbed by the materials from the rotary engine is extracted by both a water cooling system as well as the oil lubrication system, each having their own cooler or heat exchanger. The use of oil as a mechanism for extracting heat is consid erably different from the use of oil in a piston engine.

To lubricate the Wankel rotary engine, one part of the oil is injected in the air-fuel mixture to lubricate the wall of the epitrochoid surface and the seals and another part of the oil is circulated onto the shaft bearings and shot into the rotor to cool same. The most important quality which the oil should possess is the ability to contribute to the heat balance of the engine. Typi cally the oil used in a piston engine will carry only l2 percent of the heat loss that is extracted by the water cooling system. In contradistinction the oil lubricating system of a Wankel engine will carry away at least 50 percent of the heat removed from the engine by the water cooling system and will dissipate 7 percent of the total energy used by the engine. Important oil temperature variations are thus observed in service within a rotary engine. At full power, the oil in the sump can easily reach temperatures of about 150C, not withstanding external ventilation. The oil inside the rotor certainly must reach even higher temperatures.

Another problem associated with the oil lubrication system of a Wankel type engine is that of the influence of lubricating oil on the possibility of pre-ignition. The heat of the combustion process is conventionally conducted from the walls of the rotary piston so that the exposed surface of the rotor may act as a chill element i a the combustible gases in the variable volume chamher. As a result, a thin layer of such gases against the rotor remains uncombusted to contribute to lower efficiency, fuel consumption and poor emissions. If the rotor were allowed to build up heat on the exposed surface, local hot spots would result in pre-ignition or popping of the air-fuel mixture prior to suitable ignition timing. This can be very detrimental to the serviceability of the engine. Since the variable combustion chambers of a rotary engine pass over all points of the rotor housing, only a single source of ignition is required for each rotor. Any misfiring caused by hot spots or deposits may disturb the cycle harmony and thus is one of the traditional handicaps of a rotary engine.

A related problem to unnecessary heat extraction, is the emissivity level of a typical Wankel engine. The hotter the temperature of the exhaust gases, the more effective will be control of the carbon monoxide and hyrocarbons. However, due to the excessive heat loss through the oil lubricating system, the temperature of combustion is lowered and the emissions not lowered.

SUMMARY OF THE INVENTION The primary object of this invention is to provide an apparatus and particularly a coating system for the rotor of a rotary internal combustion engine, the apparatus being effective to substantially reduce heat loss through the oil lubricating system and thereby improve the fuel consumption and efficiency of the engine.

Another object of the invention is to provide a rotary internal combustion engine having means for lowering emission level, such means being primarily in the nature of a coating system of the rotor of such an engine.

Still another object of this invention is to provide an apparatus for a rotary internal combustion engine which is effective to decrease incidents of pre-ignition and insure that the combustion cycle is harmonized as predetermined.

Yet still another object of this invention is to provide a rotor for a rotary internal combustion engine which is simpler in interior design, and eliminates the requirement for an independent oil cooler.

A final object is to provide a method of constructing a rotor which employs ultra thin layers of discrete as well as graduated material mixtures to obtain improved operating results.

SUMMARY OF THE DRAWINGS FIG. 1 is a sectional view of a rotor for a typical rotary internal combustion .engine coated according to this invention and illustrating internal oil flow, the section being taken along line I-l of FIG. 2 to illustrate the internal chambers thereof;

FIG. 2 is a central iew taken transversely through a rotor embodying the features of this invention;

FIG. 3 is a schematic illustration of an improved rotary engine embodying the features of this invention;

FIG. 4 is an enlarged schematic illustration of the macrostructure of one part of the coating system, as identified at A in FIG. 1; and

FIG. 5 is a graphical illustration of the variation of horsepower, torque and fuel consumption with rpm. for a rotary engine employing the invention herein.

DETAILED DESCRIPTION The rotary internal combustion engine is unique in that the oil lubricating system is not only extremely important to the lubrication of the main rotor bearing, but the high pressure oil is permitted to circulate through a maze of internal pockets throughout the interior of the rotor and thereby serving to conduct heat from the rotor to maintain an appropriate operating temperature for the materials of the rotor. As shown in FIG. 1, the power shaft 10 has an internal longitudinal passage 11 with a radiating port 12 to introduce oil to the interior of the bearing sleeve 13 journalling the rotor. The sleeve 13 has an annular groove 14 to receive the oil from port 12 to distribute throughout the interior of the sleeve. Oil is shot into the various interior chambers 16 of the rotor by at least one other radial port 15 which is aimed to by-pass the bearing 13 (see FIG. 2).

The design of the materials for the rotor body is primarily selected with emphasis toward wear-resistance and durability to the combustion process. Accordingly, nodular cast iron has been preferred as a material selection, although the prior art has experimented with aluminum alloys and powder iron with graphite. Little attention has been devoted to the insulating value of the rotor material or any coating placed thereon. As a consequence, the rotor has become quite effective in transferring heat to the oil lubrication system immediately in contact with the interior of the rotor flanks. As mentioned, the heat lost through the oil lubricating system of prior art engines has been determined as at least 50 percent of the heat loss through the water cooling system. This constitutes at least 7 percent of the total energy supplied to the engine. This is a serious loss that eventually takes its toll in lower efficiency for the en gine.

With conventional rotary internal combustion engines, the rotor material acts as a relative chill element to hot gases immediately adjacent thereto causing a thin film of cool gases to remain uncombusted thereby contributing not only to lower efficiency, but also to higher emissions,

Rotors typically have three flanks 23 triangularly interconnected; slots 24 are disposed at the apices for receiving seals 25 which will be in dynamic contact with an epitrochoid surface 26 ofa surrounding housing 27. Combustion pockets 28 or channels are defined in each of the rotor flanks to provide for adequate compression as each chamber (20, 21 or 22) undergoes the various cycle of the engine. Some attempt has been made to increase the efficiency and power capability of the rotary internal combustion engine by redefining the variable volume chambers 20, 21 and 22 (see FIG. 3). The redefinition of the combustion pockets 28 has been undertaken, but only limited benefits can be obtained through this facility.

This invention takes a radically new approach to improving several critical aspects of the rotary engine, namely, the efficiency, fuel consumption, emission lev els and prevention of pre-ignition. To these ends, the invention requires at least two critical elements in a coating system 30 applied preferably to the rotor flanks or other outer faces, including the surfaces of the com bustion pockets 28 defined in each flank or in some embodiments the coating system can be applied to. As shown in FIG. 4, the first element is an insulating me dium 31 which can withstand the high temperature of the internal engine combustion process and be sufficiently strong to operate over a long period of engine use under dynamic conditions. The insulating medium must be capable of being applied in relatively thin layers for economy and production efficiency, and must have a high insulating value.

The second element comprises a heat quenching medium 32 which is applied about the insulating medium as an envelope to dynamically distribute heat throughout the mass of the quenching medium to prevent local hot spots that may cause pre-ignition and at the same time reduce the film of cooled gases in contact therewith. if the insulating medium was exposed to the hot gases, local hot spots would occur because of its poor heat conductivity. The exposed surface of the rotor is maintained at a higher temperature, but uniform throughout for reducing the film of non-combusted gases. As a result, the engine will have considerably hotter exhaust gases which will prove to be an advantage with respect to reducing emission levels of the engine. The housing will also operate at a higher tempera ture, but this has proved not to be a problem for the selected materials.

As a specific preferred embodiment, the rotor con' struction would comprise a nodular cast iron substrate or body 29 as shown in FIG. I having the triangulated flanks 23 with combustion pockets 28 disposed in the central area of each flank. The casting has a free-form type of interior including depending walls 40 connect ing with a central hub 41. The hub is journalled upon an oiled bearing sleeve 13. Slots 24 are defined in the apices of the casting to receive apex seal assemblies 25 therein. The relative minimum thickness 42 of the casting between the internal chambers 16 and outer exposed flank surface is about 0.02 inches. The flank surfaces are typically machined 10 mils under the final required dimension for the rotor to accommodate the coating system to be described.

The coating system consists of a first layer plasma sprayed, as a flash coating, onto the flanks 23 and pockets 28. The layer 50 consists of a l:l mixture of nickel-chromium; its thicknenss is in the range of 0.00 l0.00l 5 inches thick. It is important that layer 50 be uniform and continuous. Next a layer 51 of transition material (mixture of nickekchromium and stabilized zirconia) is plasma sprayed onto layer 50', the latter should have a thickness in the range of ().0005U.O0l inch. Some open spots in this layer are tolerable and thus the extreme thinness is serviceable. A layer 52 of stabilized zirconia is plasma sprayed thereover in a thickness range of 0.0040.0045 inches. Greater thicknesses up to 0.01 inch can be utilized, but beyond the latter problems of rotor balancing may enter.

A fourth layer 53, acting as an intermediate transition coating, is plasma sprayed over the stabilizer zirconia; layer 53 consists of a mixture of nickel-chromium and zirconia and should have a nichrome thickness in the range of 00005-0001 inches. Lastly, a layer 54 of an equal mixture of nickel-nichrome is plasma sprayed thereon in the thickness range of 0001-0002 inches.

The total coating system should not exceed 0.001 inches and none of the stabilized zirconia should be allowed to be exposed.

The insulating coating should be selected from materials having a thermal conductivity less than 20 BTU/HR/Ft. /F./in. Materials which would be excellent candidates with this in mind would comprise stabilized zirconia (having a thermal conductivity of about 7-8), thorium oxide (having a thermal conductivity of about 0.24), mica (having a thermal conductivity of about 4.8), and magnesium oxide (having a thermal conductivity of about 18). The ability to insulate against head transfer is a phenomenon that will depend upon the lattice vibration or electron energy of the crystalline structure. Accordingly, stabilized zirconia is desirable since the alpha phase has been stabilized such as by CaO to raise the alpha to beta transition temperature. Plasma spraying is very helpful since air pockets can be imported into the applied zirconia and controlled in size to increase the insulating value. The selected particles of zirconia are heated and impacted with a high force so as to form a self-fused coating and preferably should have a Rockwell C hardness of about 33 and a porosity of 6 percent.

The heat conducting means 32, which is preferably comprised of a nickel-chromium composite, is commercially referred to as nichrome. Equivalent materials can be selected from the group consisting of copper, aluminum iron, chromium or alloys of such metals. The fundamental purpose of such heat conducting means is to distribute heat across the surface of the rotor flanks and prevent pro-ignition of uncombusted gases therein.

As a result of the use of the above coating system, a large fraction of the heat normally lost through the oil lubricating system can now be put to use in the engine. This is sensed through an approximate increase in the power from the expansion of combustion gases. As shown in FIG. 5., there is a definite increase in both the torque and horsepower curves 60 for an engine having the present invention, over the similar curves 62 and 63 for a prior art engine. Maximum benefit is realized at low r.p.m. where heat transfer can be more effective with time. Similarly, the observed specific fuel consumption will be improved, as shown in FIG. 4, as represented by curve 64 for a conventionally constructed engine and curve 65 for an engine embodying this invention. This is a direct result of a reduction of the wall quenching effect so prevelent in rotary engines. The layer of unburned gases co-existing near the walls is reduced considerably.

The above benefits which flow from the new rotor structure, above described, can result in a new freedom of engine design. Since the rotor can now be well insulated, the need for oil swirling just inside the rotor flanks can be reduced or eliminated. This permits a simpler rotor design and may eliminate the need for an oil cooler normally associated with the oil lubricating system. The thermal conductivity ratio of stabilized Zirconia to cast iron is about I to 60 which insulates extremely well.

Since the oil lubricating system need only serve the bearing sleeve, the engine can then have the elements as shown in FIG. 3. The rotor can have the internal chambers rearranged so that webbing 70 can be placed to give maximum strength to the rotor with the greatest reduction in mass, such as reduction in thickness of the flank walls. Means 71, for introducing a combustible mixture into a chamber as it passes intake port 72, is shown. Dual spark means 72 is disposed adjacent the minor axis of the epitrochoid for igniting the mixture at a predetermined moment of compression. Out-take means 73 exhausts combusted gas through port 74.

Certain other methods of applying the various layers can be employed, such as sputtering or vapor deposition. In such instances, coating of the entire rotor, rather than just the flanks may be obtained provided ultra thin layers are used. One particularly unique method of preparing an insulated rotor is as follows:

I. Prepare a rotor for a rotary internal combustion engine by conventional casting techniques and define said rotor with triangularly related flanks, flat sidewalls, combustion pockets centralized in each of said flanks, and internal webbing effective to support said flanks and sidewalls on a hub with a maximum reduction of mass.

2. Provide a vapor deposition apparatus having at least two crucibles, one of which contains an adherent conductive metal for vaporization and the other containing an insulating medium vaporizable for providing an insulating coating, said apparatus having separate controls for communicating one or both of the vapors from said crucible to a deposition chamber.

3. Place said prepared rotor in said chamber and sequentially coat said rotor with five distinct layers. The first layer should consist of said adherent conductive metal in a deposited thickness of between 0.0005-0.00l5 inches.

4. While continuing to supply vapor of said adherent conductive metal to said deposition chamber, the controls are shifted to introduce simultaneously and graduated the vapor of said insulating medium. A composite transition layer is deposited having ultimately an equal mixture of said adherent metal and said insulating medium, the layer having a deposited thickness in the range of approximately 00003-000] inches.

5. Eliminate vapor communication from said adherent metal and permit solely thee vapor of said insulating medium to deposit a third layer thereon in the thickness range of approximately 00005-00] inches 6. While continuing to supply vapor of said insulating medium, the vapor from said conductive metal crucible is introduced simultaneously and graduated to ultimately provide an equal mixture of insulating medium and conductive metal to define a fourth layer in the thickness range of 0.0005-0.00l5 inches.

7. Eliminate the communication of the vapor from said insulating medium so that solely the vapor from said conductive metal is introduced for providing a final and fifth coating in the thickness range of 0001-0002 inches.

The insulating medium can be selected from the group consisting of zirconia, mica thorium oxide, mag nesium oxide and organic materials having a high resistance to temperature. The adherent metal is selected from the group consisting of copper, aluminum, iron, chromium and mixtures or alloys thereof.

I claim:

1. In a rotary internal combustion engine, a rotor journal for movement within said engine, to assist in defining a plurality of variable volume combustion chambers, the rotor comprising:

a. a metallic substrate body presenting a plurality of angularly connected outer walls each facing said chamber, said body having at least one channel interrupting each of said walls,

b. an insulating coating adherent on said walls and channels for reducing heat transfer from said combustion chambers to the interior of said substrate body, said insulating coating being selected from the group consisting of magnesium oxide, mica, expanded stabilized zirconia, and thorium oxide, said insulating coating having a thickness in the range between 0.0005 and 0.01 inches, and

c. heat conductive means covering said insulating coating effective to quench the temperature of any zone of said coating to prevent unwanted preignition ofgases within said combustion chambers, said heat conductive means comprising a coating of material selected from the group consisting of copper, aluminum, iron, nickel, chromium and alloys thereof.

2. In a rotary internal combustion engine, a rotor journalled for movement within said engine, to assist in defining a plurality of variable volume combustion chambers, the rotor comprising:

a. a metallic substrate body presenting a plurality of angularly connected outer walls each facing said chamber, said body having at least one channel interrupting each of said walls,

b. an insulating coating adherent on said walls and channels for reducing heat transfer from said combustion chambers to the interior of said substrate body, and

c. heat conductive means covering said insulating coating effective to quench the temperature of any zone of said coating to prevent unwanted preignition of gases within said combustion chambers, the insulating coating and heat conductive means are each deposited as a self-fused coating of particles, the insulating coating being comprised primarily of stabilized zirconia particles (ZrO and the heat conductive means being comprised of a composite of nickel-chromium particles, there being a gradi- 3. The rotor as in claim 2, in which said zirconia coatent layer intermediate each of said heat conductive ing is comprised of said selffused impacted particles means, insulating coating and metallic substrate providing a coating hardness of about Rockwell C 33 which is comprised of a mixture of zirconiaand an inherent porosity of about 6 percent, nichrome. 

1. IN A ROTARY INTERNAL COMBUSTION ENGINE, A ROTOR JOURNAL FOR MOVEMENT WITIN SAID ENGINE, TO ASSIST IN DEFINING A PLURALITY OF VARIABLE VOLUME COMBUSTION CHAMBERS, THE ROTOR COMPRISING: A. A METALLIC SUBSTRATE BODY PRESENTING A PLURALITY OF ANGULARLY CONHECTED OUTER WALLS EACH FACING SAID CHAMBER, SAID BODY HAVING AT LEAST ONE CHANNEL INTERRUPTING EACH OF SAID WALLS, B. AN INSULATING COATING ADHERENT ON SAID WALLS AND CHANNELS FOR REDUCING HEAT TRANSFER FROM SAID COMBUSTION CHAMBERS TO THE INTERIOR OF SAID SUBSTRATE BODY, SAID INSULATING COATING BEING SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM OXIDE, MICA, EXPANDED STABILIZED ZIRCONIA, AND THORIUM OXIDE, SAID INSULATING COATING HAVING A THICKNESS IN THE RANGE BETWEEN 0.0005 AND 0.01 INCHES, AND C. HEAT CONDUCTIVE MEANS COVERING SAID INSULATING COATING EFFECTIVE TO QUENCH THE TEMPERATURE OF ANY ZONE OF SAID COATING TO PREVENT UNWANTED PREIGNITION OF GASES WITHIN SAID COMBUSTION CHAMBERS, SAID HEAT CONDUCTIVE MEANS COMPRISING A COATING OF MATERIAL SELECTED FROM THE GROU CONSISTING OF COPPER, ALUMINUM, IRON, NICKEL, CHROMIUM AND ALLOYS THEREOF.
 2. In a rotary internal combustion engine, a rotor journalled for movement within said engine, to assist in defining a plurality of variable volume combustion chambers, the rotor comprising: a. a metallic substrate body presenting a plurality of angularly connected outer walls each facing said chamber, said body having at least one channel interrupting each of said walls, b. an insulating coating adherent on said walls and channels for reducing heat transfer from said combustion chambers to the interior of said substrate body, and c. heat conductive means covering said insulating coating effective to quench the temperature of any zone of said coating to prevent unwanted preignition of gases within said combustion chambers, the insulating coating and heat conductive means are each deposited as a self-fused coating of particles, the insulating coating being comprised primarily of stabilized zirconia particles (ZrO2), and the heat conductive means being comprised of a composite of nickel-chromium particles, there being a gradient layer intermediate each of said heat conductive means, insulating coating and metallic substrate which is comprised of a mixture of zirconia-nichrome.
 3. The rotor as in claim 2, in which said zirconia coating is comprised of said selffused impacted particles providing a coating hardness of about Rockwell C 33 and an inherent porosity of about 6 percent. 